1. Field of the Invention
The present invention relates to an electronic channel selecting apparatus. More specifically, the present invention relates to an electronic channel selecting apparatus in which any one of a plurality of channel selecting circuits is selectively brought in an active state upon application of an individual channel selection signal to the corresponding channel selecting circuit for providing a preset tuning control voltage for the corresponding channel to a tuner employing a voltage controlled variable reactance device as a tuning element.
2. Description of the Prior Art
In reception of the television broadcast, it is necessitated to select a desired channel out of several television broadcast channels. One of the typical channel selectors so far employed in selection of television channels is a rotary switch. However, a rotary switch usually makes a circuit through a mechanical touch between paired contacts performed by a manual rotating operation. For this reason a rotary switch always suffers from a poor electrical contact between the paired contacts caused by deterioration of the contact surfaces, a tiresome manual operation and a noise caused by rotating operation thereof. Another typical channel selector suitable for selection of television channels is a multi-circuit push button switch. Again, however, the push button switch involves the same shortcoming of a poor electrical contact for the same reason as that of the rotary switch.
Recently a television channel selecting apparatus for selecting television channels employing a voltage controlled variable capacitor has been proposed and widely used. Such a voltage controlled variable capacitor uses a capacitance formed at a barrier portion of a diode, variable as a function of a reverse voltage applied thereacross, and is also known as a variable capacitance diode. In such a television channel selecting apparatus, it is necessary to provide a tuning control voltage generating circuit in which any one of a plurality of storing circuits is selectively brought in an active state or a signal storing state upon individual manual selection for providing a corresponding tuning control voltage to apply the same to a voltage controlled variable capacitor employed as a tuning element of the television channel selecting apparatus. In view of implementing the channel selecting circuits by means of solid components such as voltage controlled variable capacitor, it is also preferred to implement a plurality of tuning control voltage generating circuits by means of solid state components.
A television channel selecting apparatus of a remote control type has also been proposed and in practical use. Such an apparatus is supplied with a common selection signal via a common input circuit in lieu of individual selection signals to be applied individually to the corresponding signal storing circuits. It is again preferred to provide a channel selecting apparatus in which any one of a plurality of signal storing circuits is selectively brought in an active state upon application of a common selection signal via a common input circuit as well as of an individual selection signal to the corresponding signal storing circuit for providing a corresponding tuning control voltage therefrom.
Another type of television channel selecting apparatus employing a voltage controlled variable capacitor is structured such that the bands of the television channels are switched by means of solid state components and in response to a band switching signal. More specifically, a typical television channel selecting apparatus employing a voltage controlled variable capacitor as a tuning element is adapted to be capable of receiving a UHF band as well as a VHF band which is constituted of a low VHF band and a high VHF band according to the Japanese television broadcasting standard, as well known to those skilled in the art. Thus, such a television channel selecting apparatus should be capable of selectively switching these broadcasting bands, i.e. a VHF low band and a VHF high band, and a UHF band in response to a band selecting signal, preferably with solid state components.
In summary, a television channel selecting apparatus employing a voltage controlled variable capacitor as a tuning element is preferably capable of performing various functions, such as providing a band switching signal, providing a channel selection display signal, selecting channels in response to a remote control signal, preventing malfunction of an automatic frequency tuning at the time of channel selecting, initial setting of a specified channel at the time of turning on of a power supply of the television receiver, and the like, in addition to supplying a preset tuning control voltage for the corresponding channel to a voltage controlled variable capacitance diode. These requirements make the circuit configuration of the apparatus complicated and necessitate optimized interrelationship of the circuit portions in the apparatus for performing these functions. On the other hand, if the apparatus is to be implemented employing an integrated circuit, it is imperative that these circuit portions be implemented with economy and for better performance.